Influence of ordering kinetics on dendritic growth morphology

The effect of interfacial ordering kinetics oil growth morphology is examined for undercooling, solidification of intermetallics. The focus is oil MAL which has been found to solidify into completely irregular seaweed-like morphologies at growth velocities of similar to 2 m s(-1). The transition from regular dendritic to seaweed growth in this material is simulated using a hybrid deterministic-probabilistic model of microstructure evolution, taking account of the interfacial kinetic effects. Modelling, shows that seaweed formation in intermetallic forming systems can be attributed in part to transient entrapment of the chemical and orientational disorder at the solid/liquid interface. Both types of disorder trapping give rise to strongly preferential depression of the interfacial temperature. while orientational disorder trapping also reduces the definitiveness of crystal orientation at the interface. These effects counterbalance the role of crystallographic anisotropy in promoting growth into preferred directions. and hence lead to relatively easy breakdown of regular dendritic patterns in highly ordered materials. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.